Molecular structure analysis of proteins related to human immunodeficiency virus/human T lymphotropic virus (HIV/HTLV) pathogenesis, related growth and regulatory factors, and prevention of disease: Aspects of cell-receptor binding, humoral and cellular immune response, and vaccine design are being studied by combined approaches of peptide synthesis, physiological function, and molecular modelling. Viral pathogenesis: Work on the structure and function of viral proteins and peptides has led to the findings that sequences of HIV gp4l and nef can stimulate resting normal B-cells poly-clonally to differentiate and produce IgG. We have also found that the carboxyl terminus of tat can specifically bind to cells. Detailed characterization of the mechanism and function of these reactivities are in progress. The HIV/simian immunodeficiency virus (SIV)/HTLV envelope binding sites of neutralizing, non-neutralizing, and cross-reactive antibodies have been identified and their structural and functional properties are being determined. Applications to vaccine design are being studied. U.S. prevalence of HTLV-I and HTLV-II and relation to disease: A retrospective random sampling of the U.S. population (NHANES-II), a retrospective geographic drug abuser population, and a current drug abuser population have been tested previously for HTLV-I antibody. Analyses in progress will indicate frequency of infection and its rate of change in these populations. The range of clinical manifestations of HTLV-I and HTLV-II will be monitored in the current population of intravenous drug abusers.